This is the final circuit I have, see page 5 for details:
Update 2: Somehow I managed to kill two MPSA42 transistors in the circuit. One is for soft start one is burnt when running at 300V and bearing 450mw for a to92 seems to be too much. Now I replaced all four transistors with TIP500, which can stand 400V, and they dissipates about 1w without heat sink, so I will be good for a while.
Updated again with 5 cell lipo supply, on man, what a difference. My old lambda is singing with 600v peak to peak voltage swing!
Showing how this little happily drives the ECR500 now. Scope is showing 50v/div, so it looks like 250v peak to peak playing music in my normal listening level, will distort at full output. However its the mighty inefficient ecr500, for stax normal bias version lambda, it singg without any distortion.
Schematic, note Vcc can be changed from 150v up to 300v, but current is always 6ma per channel, so loading resistor needs to be adjusted accordingly.
Input can be balanced or not, does not matter. At the output, it will always be balanced.
One concern I have is, some people like to ground all their devices together, cause ground loop noise or whatever people may call it. In this circuit, the input is floating.
needs 2v peak to peak to reach full output swing.
Testing with one channel:
[updated with edits: I raised the power supply to +300V by doing a voltage multiplier from switch power supply and feed it with 20 volts, output swing is now 600V peak to peak, with idle power consumption near 4 watts, man what a difference! ]
Recently I have been trying to work on a very cheap stax amp that aims to drive electrostatic headphones. Thanks to the help of the headfiers here, especially to Frank, who offered to send me the 6pin female connectors for free.
So far, this thing costs nothing compared to other fancy builds:
all the parts needed for this amp, excluding enclosure is around $20. So cheap that I feel many people won't even bother do look at the measurements. However the results are really good and I really like the sound of this cheap amp.
Power supply: battery or 12V supply, so it can be powered by 3 cell lipo or 12v wall adaptor. ( now I am good with 19V )
Output: 600v peak to peak.
Idle Power: 300V *12ma=3.6 watts, that translates to 6 ma per channel, and 3ma per leg of each differential pair.( surprisingly to92 package with 600mw heat dissipation is more than enough, so I am not using any head sinks at all).
Input impedance: 2k
FR: DC to 15Khz db, rolls off to -3db at 20Khz
Please offer some thoughts and comments. I need some help building the enclosure, will really appreciate if anyone can provide some resources. this thing can be made quite small so mental project enclosure is currently my top choice, just want to know how you guys drill holds for these enclosures? what tools do I need?
Edited by wdiabc - 3/31/13 at 8:50pm